SAN DIEGO — Lots of boaters and jet skiers are expected at Mission Bay through this holiday weekend. Many will rent their equipment from nearby shops such as Seaforth Boat Rentals.

“I have more reservations on the books for the Fourth of July than ever,” owner Andy Kurtz said. “So, I’m happy.”

But he’d been even happier if Seaforth didn’t have to compete with illegal rentals, typically individuals renting out their own equipment. The practice generally comes at cheaper rates, but also carries major safety risks for those involved, Kurtz said.

“We’re going to make sure you know what you’re doing before we put you on that craft,” he said. “If you’re renting from a guy off Craigslist, he’s going to say, ‘Here you go. Meet you at the launch ramp. Tell me when you’re done and I’ll pick it up.’ No instruction, no overview of how to operate that vehicle and how to do it safely.”

San Diego police and local lifeguards say the problem is worsening. They are planning to conduct extra patrols on the bay this weekend as a safeguard against illegal rentals.

“If it is an illegal rental, they will get cited, the operator, as well as the watercraft will get impounded,” San Diego police Officer Joseph Hilton said.

Police also are reminding anyone under age 40 and operating a vessel to have a California Boater Card.

To apply for a California Boater Card, visit californiaboatercard.com.